This invention relates to diacetylenes and polymers thereof. More particularly, it relates to the preparation of thin large-area single crystal films of diacetylene and of polymers thereof.
Polydiacetylenes consist of weakly coupled linear parallel chains of conjugated covalently bound carbon atoms. Polydiacetylenes are formed by a solid state reaction of adjacent monomer units in diacetylene single crystals which can be grown by a variety of approaches to achieve macroscopic form. The polymer backbone is usually represented by the acetylenic structure (I) ##STR1## where R and R' are suitably chosen side groups which vary from polymer to polymer. The fully conjugated backbone of the polydiacetylene provides a one-dimensional electronic structure.
Fully crystalline polydiacetylenes have been reported to exhibit carrier mobilities comparable to silicon or gallium arsenide. For example, the diacetylene polymer from bis (p-toluene-sulfonate) of 2,4-hexadiyne-1,6-diol (PTS) has been reported to exhibit exceptionally high carrier mobilities along its chain direction, .mu..about.20 m.sup.2 s.sup.-1 v.sup.-1. The long carrier mean free paths implied clearly follow from the full order of these polymers. This class of polymers is of value as nonlinear optical elements, as photoconductors, time-temperature indicators, photoresists, and memories. Polydiacetylenes may also have application in all optical signal processing due to the very high values of their third-order nonlinear susceptibilities .chi..sup.3 (.omega.).
The predominant physical form required for the various optical, electrical, or electronic applications for polydiacetylenes is that of a uniformly thin (.ltoreq.100 microns) large area (.gtoreq.0.1 mm on all sides) single crystal. Prior to the present invention that method disclosed in U.S. patent application Ser. No. (705,586) by M. K. Thakur, S. K. Tripathy, and D. J. Sandman entitled "Thin Large-Area Single Crystals of Diacetylenes and Polydiacetylenes and Methods for the Preparation Thereof", filed concurrently herewith, neither polydiacetylene crystals having such dimensions nor a systematic technique for preparing polydiacetylene crystals having such dimensions have been reported.
Conventional approaches of crystallization, as reported in U.S. Pat. No. 4,220,747, issued to A. F. Preziosi et al. on 2 Sept. 1980, result in crystals of uncontrollable dimensions, beset with macroscopic flaws and surface defects. Accordingly, the crystals prepared by known methods are not suitable for most existing and envisaged optical, electrical, or electronic applications. Crystal growth techniques for preparing single crystals of various inorganic materials or small organic molecules have not been successfully used to grow uniformly thin (.ltoreq.100 microns) optical quality large size crystals of organic polymers. Epitaxial methods, or the methods for lattice matching, originally developed for crystallization of inorganic solids, has also been tried for organic polymeric materials such as polyethylene, polyoxymethylene, and polydiacetylenes. These efforts have not, however, been successful to prepare uniformly thin (.ltoreq.100 microns) macroscopic single crystals of polydiacetylene. Polydiacetylene crystals grown by epitaxial methods, as reported by S. E. Rickert et al. in Mol. Cryst. and Liq. Cryst. 96, 307 (1983), are only of microscopic size, .about.1 micron.times.1 micron.times.200 angstroms.